Improvement of Fertilization Rates in Spawnings of Captive-Reared Red Telefish, Branchiostegus japonicus

Abstract

The fertilization rates during spawnings of captive-reared red tilefish, Branchiostegus japonicus are usually low (0-0.57%), when about 200 spawners are reared in a 150m³ tank without attention being paid to sex ratio or stocking density. In order to improve the fertilization rate, six spawning experiments were carried out during the spawning seasons from 1991 to 1994 using groups of one male and one, four or five female (s) . The fertilization rates in 1991 and 1994, when one male and five or four females were used, were relatively high (24.7% and 17.9%) . In contrast, no fertilized eggs were obtained in three experiments in 1992 and 1993, when the original spawners were replaced by other fish just before or in the middle of the spawning season. An experiment in 1993 was lost due to malfunction of the equipment. These results suggest that rearing one male with several females in a tank is effective to improve the fertilization rate of captive-reared red tilefish. It seems also necessary to acclimate the spawners in the tank to obtain fertilized eggs.